1. The Field of the Invention
The present invention relates to optical transceivers. More particularly, embodiments of the invention relate to devices that provide inrush current control TECs used to cool/heat lasers in optical transceivers.
2. Background and Relevant Art
Fiber optic networks use light signals to transmit data over a network. Although light signals are used to carry data, the computers and other network devices that use the data in the light signals rely on electrical signals. As a result, it becomes necessary to convert the light signals into electrical signals in order to extract and use the data. Also, it is necessary to convert electrical signals into light signals to transmit the data over the optical network. The conversion of an optical signal into an electrical signal and the conversion of an electrical signal into an optical signal is achieved using an optical transceiver.
An optical transceiver is a device that typically includes both a receiving optical sub assembly (ROSA) and a transmitting optical sub assembly (TOSA). The ROSA receives the light signal with a photodiode or other light detector, which converts the light signal into an electrical signal. The electrical signal is then amplified and further processed for use by the receiving device.
A TOSA typically includes a laser that generates the light that is launched into the optical network. When a device desires to transmit data, the light emitted by the laser is modulated accordingly. Thus, the data carried by the light signal often originates as an electrical signal and the conversion of an electrical signal into a light signal is usually accomplished using the laser in the TOSA.
Optical transceivers, such as the XFP, SFP, GBIC and other form factors, are typically required to comply with a standard. The XFP MSA, for example, has adopted the 10 Gigabit Small Form Factor Pluggable Module specification. This XFP MSA specification defines the mechanical, management, and electrical interfaces of the XFP module.
The XFP MSA specifies certain current requirements of an XFP module. Currently, the XFP MSA specification requires that current should be less than 1 amp under all conditions. Current exceeding this ceiling can have adverse effects. The XFP module itself or some of its components, for example, may be harmed by excessive current. Systems interacting with the XFP module may also be harmed or caused to malfunction by excessive current.
One of the important components of an XFP module is the laser. As is known in the art, lasers are sensitive to temperature. In fact, the wavelength emitted by a laser can vary with temperature. For at least this reason, among others, it is useful to control the laser temperature. This is done using a device such as a thermoelectric cooler (TEC), which can provide precise temperature control.
The current requirements of a TEC are often related to temperature differentials. The size of the temperature differential can have an impact on the current requirements of the TEC. When an XFP module, for instance, is initially powered on, it is likely that there is a significant temperature differential between the actual temperature of the laser and the target temperature of the XFP module. In an effort to drive the XFP to the proper temperature, an inrush current may be may be drawn by the TEC that exceeds the maximum current specified for the module.
The inrush current is a transient current that may be experienced when an XFP module is powered on or in other situations where a relatively large temperature differential is present that results in current requirements for the TEC that exceed specification.